Hitherto, a tire test (uniformity test) has been carried out for measuring the uniformity of the tire, thereby determining whether the tire finished as a final product is good or bad. For example, the measurement of the uniformity of the tire of a passenger car is carried out by using a tire uniformity testing machine (hereinafter also simply referred to as tire testing machine) including a spindle shaft that rotates while holding a tire, a load drum (hereinafter also simply referred to as “drum”) that includes an outer peripheral surface, a pressing mechanism that supports the drum for rotation, and moves the drum and the spindle shaft relatively to each other so as to press the tire mounted on the spindle shaft against the outer peripheral surface of the drum, and a pneumatic circuit that adjusts the pressure of compressed air supplied from a factory air source, and supplies the adjusted air to the tire seated on rims in accordance with the following steps.
First, the rims separated into upper and lower rims sandwich the tire that has been transported from an upstream of an inspection line. Then, the pneumatic circuit inflates the tire for a short period, thereby fixing the tire to the rims, and then maintains an internal pressure of the tire at a test pressure. The pressing mechanism presses the outer peripheral surface of the drum to the tire having the internal pressure maintained at the test pressure as described before, and forward rotates the tire. The uniformity of the tire during the forward rotation is measured first. Then, the spindle shaft passes through a temporary stop state, and backward rotates the tire, and the uniformity of the tire is also measured during the backward rotation.
When the rotation of the tire stops in the state where a certain pressure is applied to the tire, in other words, in a state where the load drum and the tire are in contact with each other, a recess of the tire generated by the pressure of the load drum later becomes a residual recess in this measurement method of the tire uniformity. It takes a time for the residual recess to be restored to an original state, and when the uniformity is measured while the residual recess remains, the residual recess may largely affect precision of the measurement.
As a solution to this problem, for example, a technology disclosed in Patent Document 1 is mentioned. Patent Document 1 proposes a highly precise measurement of the tire uniformity without the deformation of a tire including pressing a load drum against a tread surface of the tire, then rotating the load drum in a predetermined direction, and, then, separating the tread surface of the tire from a contact surface (simulated road surface) of the load drum when the rotation of the load drum is to be inverted, thereby bringing the tire and the load drum in a non-contact state, in other words, in a separated state.
However, Patent Document 1 does not describe how to cause the operation of inverting the rotational direction of the tire and the operation of separating the tire and the load drum from each other to cooperate with each other when the tire uniformity is measured while the tire is backward rotating. Moreover, the measurement method for the tire uniformity disclosed in Patent Document 1 inverts the rotation of the load drum in a state where the tire and the load drum are not in contact with each other, and a power source such as a motor needs to be provided for the load drum for inverting the rotation, resulting in an increase in the cost of the device. If the load drum is inversely rotated by inverting the rotational direction of the tire, the rotational direction of the tire is inverted (backward rotation) while the load drum maintains the rotation in the same direction (forward rotation) by inertia, then, the tire and the load drum are again brought in contact with each other, and a “slip” may be generated between the rims for holding the tire and an inner diameter of the tire in contact with the rims, in other words, a “displacement” may be generated between the tire and the rims. If the uniformity during the backward rotation of the tire is measured while the displacement is generated between the tire and the rims, it is hard to measure the LFV and the conicity at a desired precision.